Exposure triangle explanation please.

Started Jul 9, 2013 | Questions thread
Jeff
Veteran MemberPosts: 4,470
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Re: Not exactly
In reply to texinwien, Jul 10, 2013

texinwien wrote:

TTMartin wrote:

texinwien wrote:

TTMartin wrote:

Your definition of exposure works for a film camera with no film in it.

It works for all cameras - for film cameras with film in them and for working digital cameras.

All of the things you say are photographic exposure can be done, shutter speed and aperture, etc. And yes, the empty back of the camera was exposed to light, but, there was NO PHOTOGRAPHIC EXPOSURE.

Wrong - I just have an exposure on a highly insensitive medium

In other words one with an extremely low ISO

I'd call it an ISOless medium with a very low (and unchangeable) sensitivity. As a thought exercise, though just about every medium has some sensitivity to light.

If I ramp up the exposure by, say, using a magnifying glass to concentrate sun rays onto a small spot on a piece of ordinary wood, I can leave a mark on that wood. In a sense, the wood is photosensitive, although nowhere near as photosensitive as regular photographic film.

Now, if I put the same wood in my film camera and activate the shutter, it's highly unlikely that the wood will be visibly changed. The exposure took place, but the medium was so insensitive that no information was recorded.

You can not have photographic exposure void of a photographic medium.

This is just wrong, and really, it's beside the point. See again the article on exposure and the equation that determines photometric exposure. All that is required is a plane on which the light will fall / be collected. Whether that plane is at all photosensitive is beside the point.

Whether the plane is photosensitive is the entire point of PHOTOGRAPHIC EXPOSURE.

Practically all planes are photosensitive. Some are just more sensitive than others.

Again, you have defined exposure, just NOT photographic exposure.

There is only exposure. There is no special photographic exposure. There is light, there is a photosensitive plane on which it falls. We just have to make sure that we adjust the exposure parameters (shutter speed, aperture and scene luminance) such that the medium is properly exposed, given its photosensitivity.

And again, if changing the ISO setting on your camera doesn't affect the sensitivity of the light-gathering medium (the sensor), of what use is ISO as a concept? If ISO doesn't have any relation to the sensitivity of the medium, what good is it to us?

What I care about is the final image. I don't have a photograph until I have a final image.

I need enough exposure to render a usable image on whatever medium I'm working with - whether that's film, wood, halide covered bedsheets (actually saw this done once), or a digital sensor.  How much exposure do I need to render a usable image?

For better or worse, ISO is the calibration of choice. What would you propose in its place?

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Jeff
http://www.flickr.com/photos/jck_photos/sets/
You don't make a photograph just with a camera. You bring to the act of photography all the pictures you have seen, the books you have read, the music you have heard, the people you have loved.” -- Ansel Adams

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